Feeding normal adult mice with small dietary quantities of protein antigens resulted in partial to complete absence of antibody formation to subsequent parenteral immunization with specific antigen in adjuvant. Studies will pursue characterization of suppressor cells induced in spleen by antigen feeding, evaluate the maturational basis for the absence of feeding-induced unresponsiveness in newborn mice, determine characteristics of antibody responses in animals recovering from feeding-induced unresponsiveness, and examine the effects of feeding specific antigen to immune mice.